Tesla Power Wall

[apostolakisl]

For my office, it is necessary to have backup electricity.  For the past 18 years I have used 4 big lead acid batteries in a purpose built cabinet with inverter/auto switching.  It is not a UPS, however, if power goes out, it takes a few seconds to switch.  Anyway, the lead acid batteries have died for the second time and it costs about $1000 to replace them.

I have considered switching to a Tesla Power Wall.  It has waaaay more capacity and is micro second switching time.  Plus it can be cycled thousands and thousands of times as opposed to lead acid which die after a couple hundred.  Of course the power wall costs about $6000.  

But here is the thing, I am on commercial billing with peak kw plus kwh.  If you drop below 10kw on your 15 minute running avg peak, you pay roughly 9c/kwh and that is it.  If you are above 10kw, then you pay a lot more.  You pay about $14/kw plus about 5c/kwh.  I have done a pretty good job at reducing demand.  Compared to the people I bought the space from, I have cut my power in half but replacing all lights with led, replacing the hvac, and spray foam insulating.  But still, I am typically between 12 and 16kw peak.  I am looking at using the power wall to feed into my system when I go over 10kw and hopefully get most of my months below 10.  

The power wall, as far as I can tell, does not have switching software that does this specifically.  However, I have a number of items in my office which have high demand, but don't run often.  I was thinking if I just put those items on the power wall that I can drop my peak by 3 to 4kw without consuming all the energy by the end of the day and then letting it charge at night.

In short, the power wall is a $5000 extra investment (since I won't need the lead acid batteries).  I wrote a spreadsheet for excel which calculates my electric bill all the different ways.  And holy smokes are there all kinds of if/then scenarios with a power bill.  You should see the excel equation, it is an impressive one at several hundred characters long.  Anyway, if I knocked the peak by 3kw I would save about $800/year.  I could probably save a couple hundred more by nixing my employees from using those damn space heaters.  You would think my 100 degree summers would be the ugliest months, but it is actually the winter months and I'm pretty sure that is the reason.

Thoughts?

[larryllix]

I did a few calcs when these first came on the scene. At 10 times the storage cost per kWh the 500-600 vdc is had to deal with. This may have changed but the Power Wall could not handle the peak power that a normal household would demand. Even with demand TOU shifting the cost could never justify the difference in energy rates between the times.

More, and more recent, evaluation would be needed but a few years back it was a pipe dream, economically.

[apostolakisl]

7 minutes ago, larryllix said:

I did a few calcs when these first came on the scene. At 10 times the storage cost per kWh the 500-600 vdc is had to deal with. This may have changed but the Power Wall could not handle the peak power that a normal household would demand. Even with demand TOU shifting the cost could never justify the difference in energy rates between the times.

More, and more recent, evaluation would be needed but a few years back it was a pipe dream, economically.

If I drop my peak by 3 to 4kw, it would have been $800 less e- bill last year.  It would have been a couple hundred more but for the 3 months where my staff ran multiple 1500 watt space heaters on their feet making it impossible to get below 10kw.  The key is to get below 10kw.  The bill drops by about 40%.  So last year I only had 4 months that I could have done that.  But like I said, I think I could get 10 months under that number with some attention to detail (not running space heaters but rather just turning up the regular heat).  That gets this thing down to about a 5 year roi.  And it holds a good bit of kwh.  It is rated at 5kw continues output 13.5kwh storage.  I'm not going to run hvac on it, but I can easily run everything else for days at those numbers.  I only really need about two hours of output at 2kw to more than cover my needs.

[Scottmichaelj]

If I drop my peak by 3 to 4kw, it would have been $800 less e- bill last year.  It would have been a couple hundred more but for the 3 months where my staff ran multiple 1500 watt space heaters on their feet making it impossible to get below 10kw.  The key is to get below 10kw.  The bill drops by about 40%.  So last year I only had 4 months that I could have done that.  But like I said, I think I could get 10 months under that number with some attention to detail (not running space heaters but rather just turning up the regular heat).  That gets this thing down to about a 5 year roi.  And it holds a good bit of kwh.  It is rated at 5kw continues output 13.5kwh storage.  I'm not going to run hvac on it, but I can easily run everything else for days at those numbers.  I only really need about two hours of output at 2kw to more than cover my needs.

While I can appreciate the effort, but is it really worth it? Does the “effort” outweigh the “savings”? What happens if you add employees or demand increases? What about the actual office equipment? Could you cut energy there? Sure that’s an initial investment but would it overall lower power consumption? Is it not possible for a few solar cells on the roof? Get a Fed tax break (USA) and then as needs change you can ramp up easily? Maybe the space (if renting) would give you a break when you move or take them with you. Not sure where your located but remember hardware and utilities are a business expense (at least in the USA) so while that helps too at 20% tax rate so is that $800 really $800 or only $600? Just my thoughts, no one else’s

[apostolakisl]

1 hour ago, Scottmichaelj said:

 

While I can appreciate the effort, but is it really worth it? Does the “effort” outweigh the “savings”? What happens if you add employees or demand increases? What about the actual office equipment? Could you cut energy there? Sure that’s an initial investment but would it overall lower power consumption? Is it not possible for a few solar cells on the roof? Get a Fed tax break (USA) and then as needs change you can ramp up easily? Maybe the space (if renting) would give you a break when you move or take them with you. Not sure where your located but remember hardware and utilities are a business expense (at least in the USA) so while that helps too at 20% tax rate so is that $800 really $800 or only $600? Just my thoughts, no one else’s

 

Well the $6000 for the Tesla power wall gets written off immediately I do believe with the new tax laws.  So it would be moving a write off forward, so for the most part a wash but probably slightly in favor of spending the money now since the cost of money is likely going up and there is likely to be a little more inflation in the future.  But that really isn't going to be very significant one way or the other.

The point here is that I have to have backup electricity no matter what.  I feel like the $1000 for the lead acid batteries is just sinking money into a hole.  Lead acid batteries are just crap in general.  They can only serve a very limited role and have no capacity for ROI at all.  I feel like the $6000 for the power wall gives me a much more useful power supply that can actually turn a slight profit, rather than just cost me.  And give me 20 or 30 times more capacity.

[Mustang65]

I have an RV with 250Watts of SOLAR and (2) 6 volt Trojan T145 (260Ah) batteries, setup for dry-camping and keeping my batteries topped off. They are on year 6 and still performing very well. Granted the current Ah's are not what they were when they were new, but they still perform and meet our needs. The lifecycle for these batteries is about 1200 - 1500 cycles. Since this technology has been around for a century there is a lot of data to back them up, unfortunately, the jury is still out for the newer LifePO4 technology.

The biggest issue that I have is that the LifePO4 industry is promoting 3K - 5K cycles, well yes that is true... they will make it to 3K - 5K cycles, but what they fail to tell you up front is that those numbers can only be reached in a lab environment that is controlled 24/7. My RV is not the PERFECT LifePO4 environment, with temperature swings that can be 30 degrees a day between the high and low temperatures in the front storage compartment... but the resellers fail to mention these facts.  Take a look at the attached independent test results for the LifePO4  and flooded battery life cycles. See what part of the chart your LifePO4 battery system would be.

Personally, with either power system, I would definitely go with SOLAR. Install SOLAR and make sure it is a system that you can keep adding panels to. Not sure as to what your net-metering plan is. If it is not acceptable, go with an off-grid / grid tied system. Best of both worlds.